1. Field of the Invention
This invention relates to new antibacterial agents which interfere in bacterial cell wall synthesis.
2. Brief Description of the Art
Many antibacterial agents owe their selective toxicity to the fact that their targets are structures which are only present in the sensitive bacterium. One of these structures is peptidoglycan a cell wall polymer which plays a vital role in protecting bacteria from lysis. A number of agents, e.g., .beta.-lactams, bacitracin, and flavomycin, interfere with the assembly of this polymer by inhibiting enzymatic reactions involved in the final stages of assembly.
Peptidoglycan biosynthesis involves a precursor, UDP-MurNAc-Ala-D-Glu-Lys-D-Ala-D-Alanine that is biosynthesized in a multienzyme pathway which terminates in the addition of D-Alanine-D-Alanine to the UDP-MurNAc-tripeptide. The formation of D-Alanyl-D-Alanine is catalyzed by D-Alanyl-D-Alanine ligase (synthetase). It is known that inhibition of D-Alanyl-D-Alyanyl ligase will terminate peptido-glycan biosynthesis resulting in vivo in bacterial cell lysis. Such inhibitors can serve as anti-bacterials. For example, D-Cycloserine, a D-Alanine mimic, is a reversible inhibitor of the ligase at both the donor and acceptor sites and is the most potent ligase inhibitor described heretofore, and is a potent antibacterial. (F. C. Neuhaus et al., Biochemistry 3, 471-480 (1964)).
Dipeptide analogs of D-Alanyl-D-Alanine are also known to be inhibitors of ligase. (F. C. Neuhaus et al., Biochemistry 8, 5119-5124 (1965), and F. C. Neuhaus and W. P. Hammes, Pharmac. Ther. 14, 265-319 (1981)).
With this background, the search for newer and more effective antibacterial agents which are ligase inhibitors, is a continuing one.